They claim 129 dB max SPL @1m for the 8". I find that hard to believe.
It looks like that’s a standard sound pressure rating for lots of the powered PA speakers. Seems dubious to me, that’s really pretty loud, about twice the apparent loudness of a typical hard rock concert, and half the volume of the loudest concert ever recorded. Of course, this is also 1m from the speaker.
Nearly all of the manufacturers claim that SPL across a wide range of speakers, though, so maybe I am missing something.
Whereas for comparison an Ampeg BXT-410 4x10 cab has a max SPL of 127dB.
I’m reeeeeeally, really skeptical of these PA numbers. I bet they are theoretical.
I wasn’t following this thread. What device are we looking at?
It’s possible to write a spec number for almost anything you want. Rarely does anyone specify the other conditions of the test. SPL is frequency dependent. At what frequency was the measurement made? Everything in audio is time duration dependent. How long can it produce that level? Was the number measured or extrapolated from a lower measurement and scaled up based on some theory? If the number was scaled up, has power compression been taken into account? Or other nonlineatities?
A common industry practice among reputable manufacturers is to drive a loudspeaker with pink noise with a crest factor of 6dB for long periods of time to determine the average power that it can take, limited by overheating. Then they will extrapolate the peak power to be 4x the average power based on the 6dB crest factor. Someone may take that peak power number and apply it to the sensitivity (SPL at 1W 1 meter) and get their peak SPL number that way.
Anywhoo, except for the top end manufacturers, specs often mean nothing.
A woofer’s short term instantaneous peak level is limited by the excursion distance the cone is able to travel before the coil pops out of the gap and never goes back.
Sound levels drop according to the inverse square law due to the formula for the surface area of a sphere increasing as the radius (distance from the speaker) increases. The easy way to calculate that is to subtract 6dB every time you double the distance. If you are getting 100 dB at 1 meter, you will get 94 dB at 2 meters and 88 dB at 4 meters and so on.
I couldn’t find an actual data sheet on the Headrush Frfr-108. The 129 dB number is going to be the nominal level across its frequency range that they say goes down to 52Hz. The question is, how much has the level dropped by the time you get to 52 Hz?
It’s common to see people measure usable frequency range at the -10 dB point.
If you ignore that this is an FRFR for a moment, this is basically the same thinking of whether you generally want an 8” cabinet or a 4x10” cabinet. The FRFR won’t perform any better than an 8” bass cabinet made for bass. They aren’t using a magic 8”.
My theory (and I have no reason for this other than the number is so high for so many of them) is that across the board, manufacturers simply calculated based on peak amp power versus speaker sensitivity. Which would yield the maximum possible value at whatever the mystery optimal frequency was with everything else being perfect.
Four 5" drivers have the same surface area as a 10" driver and I’ve seen properly designed 5" drivers outperform what you typically see in terms of low frequency limit. Not many companies pay the extra $ for something high performing in that range. PJ may have a cool boutique niche here.
It should be! That’s the equivalent surface area of a 3x10 or more pushing air. I don’t know what they are doing, but if I were designing a cabinet like that I’d want to cross it over to use fewer drivers as the frequency range goes up. I’d probably have a full set, a range for 4x5 and a range for 1x5. If the wavelength of the tone gets short compared to the distance between drivers, they start to cancel each other out instead of working together. Designed well, this box could give any FRFR cabinet a run. @terb
Thanks man, that explained it a lot to me. I’ll be visiting the Bassmatters.nl store some where next summer, to see if I can find and test a pedal or two. Now at least I know what to look for, before giging begins.
At home practicing, writing and recording is fine for now. I’ve almost got the sound allready I’m looking for.